The present invention relates to a container used for the storage of a high purity liquid chemical, which is used in the fields of semiconductors and liquid crystals as well as a method for discharging the high purity liquid chemical from the container. The rule for designing, for instance, integrated circuits have increasingly required a high degree of miniaturization of these semiconductor devices because of the recent rapid progress in the electronic devices. High purity liquid chemicals such as photoresist liquids used for such fine patterning techniques not only should possess excel lent fundamental characteristics, but also should not give rise to any quality deterioration during the storage and transportation thereof. The term xe2x80x9cquality deteriorationxe2x80x9d herein used means, for instance, an increase in the amount of impure fine particles in a photoresist liquid, degeneration of components thereof, quantitative changes in the composition, an increase in the quantity of impure metal elements or deterioration of light-sensitive components due to irradiation with light rays. The increase in the quantity of fine particles in such a photoresist liquid and the degeneration of the components thereof are mainly caused by dissolution of some components present in the container material into the photoresist liquid. If such a photoresist liquid is applied to a substrate to form a photoresist film, pinholes are formed on the substrate. In addition, the quantitative changes in the composition of the liquid are resulted from the permeation of an organic solvent present in the liquid into the exterior through the wall of the container. At this stage, the liquid entrains a change in its viscosity and the thickness of the resulting photoresist film is correspondingly changed.
The quality deterioration of these photoresist liquids has serious adverse effects on the quality of the resulting semiconductors and liquid crystal displays and yields thereof and would shorten the lifetime of the liquid per se.
There has been known the term xe2x80x9ccleannessxe2x80x9d as an indication for showing the extent of the quality deterioration due to any release of impure fine particles from a container during the storage of a photoresist liquid in the container over a long time period. The cleanness is evaluated by storing ultra high pure water or a photoresist liquid in a container to be examined for a predetermined period of time and then determining the number of fine particles, whose particle size is not less than 0.2 xcexcm, present in 1 ml of the liquid stored in the container. More specifically, the cleanness can be defined by the following equation:
Cleanness (number/ml)=[c(number)xc3x97a/2(ml)]/[b(ml)xc3x97a(ml)]xe2x80x83xe2x80x83(1)
In the equation (1), a represents the volume of the container; and b is the quantity of the liquid content taken from the container to be examined. First of all, the sample liquid for determining the initial cleanness of the liquid is taken from the container according to the following method. To a test container having a volume of a (ml), there is added ultra pure water or a photoresist liquid in an amount of a half of the volume, a/2 (ml), of the container, followed by shaking it for 15 seconds, allowing it to stand for 24 hours and then collection of a sample liquid. The container used for the determination of the initial cleanness is tightly sealed with a plug, then allowed to stand for a predetermined period of time and thereafter rotated three turns without forming any air bubble, followed by collection of a sample liquid used for the evaluation of the cleanness after storing the water or the photoresist. In the equation, c represents the number of fine particles, as determined using a particle counter, which are present in the whole liquid sample and have a particle size of not less than 0.2 xcexcm. Thus, the initial cleanness and that determined after the storage over a predetermined period of time are calculated on the basis of the number of fine particles. In this respect, the lower the numerical value indicating the cleanness, the higher the quality of the photoresist liquid. If the cleanness is less than 100 particles/ml, such a liquid chemical can stably be stored without causing any quality deterioration of semiconductors and liquid crystal displays (LCD) and any reduction of the yield thereof.
As containers for storing photoresist liquids and related liquid chemicals, there have in general been used, for instance, glass containers, metallic containers and containers produced from monolayer polyethylene (PE) resins. However, the glass and metallic containers cannot ensure a high cleanness of the contents thereof since sodium ions are released from the glass container and each metal container releases ions of the corresponding metal constituting the container, such as iron ions. Moreover, a conventional container, formed from a polyethylene resin to which a composition having barrier properties is added, has a low cleanness. If a light-shielding pigment and a pigment dispersant are added to this polyethylene resin having a low light-shielding effect, the cleanness of the resulting container would be further impaired. The container for storing a photoresist liquid should have a good cleanness, a light-shielding effect and solvent-barrier properties and accordingly, all of the foregoing containers are not preferably used. In addition, other problems arise, for instance, the glass container is apt to be easily broken and the metal containers are heavy and thus inconvenient to handle.
The present invention has been developed for solving the foregoing problems associated with the conventional containers for storing and transporting high purity liquid chemicals and accordingly, it is an object of the present invention to provide a container, which never deteriorates the quality of high purity liquid chemicals such as photoresists during the storage and transportation thereof, which is hardly broken and which is also light-weight. Moreover, it is another object of the present invention to provide a method for easily and safely discharging such a high purity liquid chemical from the container for storage.
The following is the description of the present invention developed for achieving the foregoing objects. The invention will be described herein with reference to the accompanying drawings corresponding to embodiments of the invention.
As shown in FIG. 1, the container 1 for storing a high purity liquid chemical according to the present invention is one obtained by blow molding an inner layer 3, which consists of a high purity resin comprising at least one member selected from the group consisting of olefinic polymers of ethylene, propylene, butene-1, 4-methyl-pentene-1, hexene-1 or octene-1 and copolymers of ethylene and olefins other than ethylene; an intermediate layer 4 of a solvent-barrier resin, which comprises at least one member selected from the group consisting of polyamides, polyvinyl alcohols, poly(ethylene-co-vinyl alcohols), polyesters and polyphenylene oxides; and an external layer 5 consisting of a light-shielding substance-containing resin composition. The container 1 has the lowest absorbance for the whole layers 3, 4 and 5, as determined at a wavelength of not more than 400 nm using a spectrophotometer, equal to not less than 2.0; an absorptivity coefficient as determined at a wavelength of 400 nm, i.e., the absorbance at that wavelength for the whole layers 3, 4 and 5 of the container 1 divided by the thickness of the layers 3, 4 and 5, equal to not less than 1.5 mmxe2x88x921; and an absorptivity coefficient as determined at a wavelength of 600 nm equal to not more than 1.5 mmxe2x88x921. The container 1 is preferably provided with a grip 2.
The following is the description of the method for discharging a high purity liquid chemical 15 according to the present invention, in which the container 1 of the invention is used. The invention will be described with reference to the accompanying drawings corresponding to embodiments of the invention.
As shown in FIG. 2, the method for discharging a high purity liquid chemical comprises the steps of tightly accommodating, in a protective pressure container 12, 13, an inner container 1 from which one end of a liquid-discharge pipe 10 is guided to the exterior of the inner container 1, while the other end of the pipe is inserted into the inner container 1 down to the bottom thereof and which is filled with the high purity liquid chemical 15; and discharging the liquid chemical 15 through the liquid-discharge pipe 10 by the action of the pressure of a gas supplied from a pressure source 6 connected to the protective pressure container 13. The protective pressure container 12, 13 is not one made of any particular material inasmuch as the material can withstand a gas pressure of 0.1 to 3.0 kg/cm2, since the container does not come in direct contact with the liquid chemical.
According to another embodiment, the method for discharging a high purity liquid chemical comprises, as shown in FIG. 3, the steps of tightly accommodating, in a protective container 22, 23, an inner container 1 from which one end of a liquid-discharge pipe 10 is guided to the exterior of the inner container 1, while the other end of the pipe is inserted into the inner container 1 down to the bottom thereof and which is filled with the high purity liquid chemical 15; and discharging the liquid chemical 15 through the liquid-discharge pipe 10 by the action of a pump 16 disposed in the course of the path for discharging the liquid chemical. A filter 14 is preferably connected to an open port 19 of the container 23.
A further embodiment of the method for discharging a high purity liquid chemical comprises, as shown in FIG. 4, the steps of accommodating, in a protective vessel 32, 33, in an inner pressure container 1 from which one end of a liquid-discharge pipe 10 is guided to the exterior of the inner container 1, while the other end of the pipe is inserted into the inner pressure container 1 down to the bottom thereof and which is filled with the high purity liquid chemical 15; and discharging the liquid chemical 15 through the liquid-discharge pipe 10 by the action of the pressure of a gas supplied from a pressure source 6 connected to the inner pressure container 1.
The inner container 1 for accommodating the high purity liquid chemical 15, as shown in FIGS. 2, 3 and 4, is preferably the container for storing a high purity liquid chemical as shown in FIG. 1.